Field of the Invention
The present invention relates to a method of writing/reading data into/from a flexible disk and an apparatus for effecting the same, and more particularly to a method and apparatus suitably for writing/reading data at a high density onto/from a flexible disk.
With conventional flexible disk drives, a recording track on a flexible disk consists of a plurality of sectors and data read/write is done with respect to each of the sectors.
FIG. 1 shows a circular recording track on the flexible disk extended linearly. As seen, one circular recording track on the flexible disk consists of sectors S1 to SN. All these sectors S1 to SN have a format similar to that of the sector S1 which is shown by way of example. Namely, each of the sectors S1 to SN consists of an ID field 101 carrying an address of the sector, and a data field 110 where data are actually written. Further, the ID field 101 has a gap area G2 and an ID area I where the address is written. The data field 110 consists of a gap area G3, data area D where data are actually written, and another gap area G4. In FIG. 1, G1 indicates a leading gap area of the recording track, and G5 indicates the final gap area. The gap areas G1 to G5 serve to prevent any interference between data on the data areas.
The magnetic head of the flexible disk drive is composed of a read/write core and erase cores. FIG. 2 (a) is a perspective view of a conventional magnetic head. As apparent from this Figure, read/write core 203 and erase cores 204a and 204b are provided between sliders 201a and 201b, the slider 201a having a groove 202 formed therein. Also, the read/write core 203 is provided with a read/write coil 205 and a read/write core gap 207. Further, the erase core assembly 204 has an erase coil 206 and erase core gaps 208a and 208b. FIG. 2 (b) is a view, enlarged in scale, of the read/write core gap 207 and the erase core gaps 208a and 208b. When data is to be recorded, the data signal is supplied to the read/write coil 205, so that a magnetic field is produced in the read/write core gap 207. Thus, the data is written on the flexible disk. When a recorded data is to be read from the flexible disk, the data causes the magnetic field in the read/write core gap 207 to be changed. This change of magnetic field is detected by the read/write core 203, producing a read signal in the read/write coil. In FIGS. 2 (a) and (b), the arrow R indicates the revolving direction of the flexible disk.
The erase cores 204a and 204b operate, at the time of a data write, to erase in a DC manner the opposite lateral sides of the data field 110 having been rewritten by the read/write core 203. More specifically, as shown in FIGS. 2 (a) and (b), erase core gaps 208a and 208b are disposed in positions, respectively, slightly displaced from the opposite sides of the read/write core gap 207, so that after the data field 110 within a sector on the recording track of the flexible disk is rewritten, the rewritten data field 110 is erased at the opposite side thereof in DC manner by the erase core gaps 208a and 208b.
The erasure in a DC manner of the rewritten data field 110 at the opposite sides thereof is intended for ensuring the interchangeability of flexible disks between different flexible disk drives. Thus, the data not yet rewritten is prevented from remaining at any one side of the data field 110 in the sector due to any slight positioning error of the magnetic head of the flexible disk drive, and the interchangeability of flexible disk between different flexible disk drives is provided.
FIG. 3 shows in detail the contents of the sector S1 shown in FIG. 1. In FIG. 3, a PLL (phased locked loop) SYNC area PS1 (not shown in FIG. 1) is shown between the gap area G2 and ID area I, and PLL SYNC area PS2 is between the gap area G3 and data area D. These PLL SYNC areas PS1 and PS2 are necessary for putting the synchronization circuit into operation when an address written in the ID area D and data written in the data area D are to be read. Also, FIG. 3 shows an area E having been erased by the erase core gap. The sectors S1 to SN of the above-mentioned configuration are formed in all the recording tracks of the flexible disk through a process called "initialization".
FIG. 4 shows a flexible disk having data previously written in the data area D thereof and which has data in the sectors of the recording track rewritten by another flexible disk drive. In the case where another flexible disk drive is used to write data into a sector, the sector where the data is to be written is sought by reading the ID field of that sector and the predetermined data is written into the data area D of the sector. If there is any slight mismatching of the magnetic head with respect to the recording track, the write position is shifted so that the PLL SYNC area PS2 and data area D are deviated from the other areas as shown. For making such shift allowable, an area to which a new write is made is erased at the opposite sides thereof by the erase head core.
Generally, the distance l between the read/write core gap 207 and erase core gaps 208a and 208b of the magnetic head shown in FIGS. 2 (a) and (b) is selected to be extremely short in order to make the gap areas G1 to G5 shown in FIG. 3 as narrow as possible. The reason why the gap areas G1 to G5 are made narrow is to maximize the recording capacity of the flexible disk. Since the read/write core gap 207 and erase core gaps 208a and 208b are provided in proximity to each other, the following phenomenon will take place when a DC field, required for the erase operating done simultaneously with the data write operation, is applied to the erase core gaps 208a and 208b. Namely, the leakage flux is added to the magnetic flux produced by the read/write core gap 207. Thus, the magnetic flux produced by the read/write core gap 207 according to a write data instruction is disturbed. As a result, when data written on the flexible disk is read by the read/write core 203 to produce a read amplitude, the waveform A is produced as shown by the dash line in FIG. 5. Influenced by the leakage flux from the erase core gaps 208a and 208b which have been described above, the waveform A is deviated from a normal waveform B, free from the leakage flux, which is shown with a solid line in FIG. 5. Consequently, the peaks P1' and P2' of the waveform A are shifted from the peaks P1 and P2 of the waveform B, and this peak shift has been a cause of the misrecognition of reproduced data.
As shown in FIG. 4, the PLL SYNC area PS2 and data area D in each sector of a flexible disk where data have been rewritten are superposed on the data that has previously been recorded; i.e. (what is known as an "overwrite" occurs on the flexible disk. In this case, the area on which data is written will contain an erased area E. As the result, the following problem will arise. Generally speaking, a flexible disk comprises a recording medium of which the coercive force is large to implement a high-density recording. Also, the erased area E is magnetized only in a single direction because it is erased in DC manner by the erase cores 204a and 204b described above. Thus, for overwrite to be made on an erased area E magnetized only in a single direction where the coercive force is large, it is necessary to increase the write current of the read/write core 203. More particularly, it is necessary to produce in the read/write core gap 207 a magnetic flux of a sufficiently high density to write data. However, if a magnetic flux of a sufficiently high density is created in the read/write core gap 207, the magnetic flux will leak at a portion of the read/write core 203, causing a reduction of the resolution of the recording characteristic, with the result that the recording density is decreased.
As described above, the prior art has a problem in that high density recording cannot be attained because of the influence of the addition of the magnetic flux of the erase core gap to that of the read/write core gap and of the influence of the leakage flux from the read/write core.